A tumor is developed by uncontrollable disordered abnormal cell proliferation. Especially, if this tumor shows a destructive growth, invasiveness and metastasis, it is regarded as a malignant cancer. Invasiveness is a character to infiltrate or destroy surrounding tissues, and in particular, a basal layer forming a boundary of tissues is destroyed by the character, resulting in the local spread and sometimes inflow of a tumor through circulatory system. Metastasis means the spread of tumor cells from the original birthplace to other areas through lymphatic or blood vessels. In a broad sense, metastasis also means the direct extension of tumor cells through serous body cavity or other space.
These days, surgical operation, radiotherapy and chemotherapy are widely used for the treatment of cancer singly or jointly. The surgical operation is a way to remove diseased tissues. Thus, tumors in specific regions such as breast, colon and skin can be effectively removed by the surgical operation. However, a tumor in vertebra or dispersive tumor like leukemia cannot be properly treated by the surgical operation.
Chemotherapy blocks cell replication or metabolism, and has been used for the treatment of breast cancer, lung cancer and testicular cancer. Though, patients with cancers who have been treated by chemotherapy have seriously suffered from the side effects of systemic chemotherapy. Motion sickness and vomiting are common but serious examples of all. The side effects of chemotherapy can even affect the life of a patient since they might drop the adaptability of a patient rapidly. Besides, DLT (Dose Limiting Toxicity) is also one of major side effects of chemotherapy, which draws a careful attention in the administration of a medicine. Mucositis is an example of DLT against anticancer agents such as 5-fluorouracil which is an antimetabolic cytotoxic agent, and methotrexate, and anticancer antibiotics like doxorubicin. If a patient suffers seriously from such side effects of chemotherapy, he or she should be hospitalized and given an anodyne for reducing pain. So, side effects of chemotherapy and radiotherapy are the biggest problem for the treatment of cancer patients.
Gene therapy is a method to treat or prevent diseases caused by the genetic variation in human cells, for example various genetic disorders, cancers, cardiovascular diseases, infective diseases, and auto-immune diseases, by taking advantage of DNA recombination technique, that is, a therapeutic gene is inserted into a patient to correct genetic defect or to promote or add functions of cells. More precisely, gene therapy is to treat a disease by sending a therapeutic gene to a target organ in order to induce the expression of therapeutic or normal protein in damaged cells. Gene therapy has advantages such as excellent specificity and improvement of recovery rate and speed, which are difficult to be regulated by other medicine, which enables long-term administration. Gene therapy is not for treating symptoms of a disease but for curing or eliminating the cause of the disease. For the success of the therapy, it is important to deliver a therapeutic gene to a target cell to improve its expression rate, which is essential technique in gene therapy.
A gene carrier is a necessary mediator for the insertion of a therapeutic gene to a target cell. An ideal gene carrier has to be no harmful for human, mass-produced, has to carry a gene to a target cell efficiently and has to express the gene continuously. Preparation of a Gene Carrier is a Core Technique in Gene therapy. Most representative gene carriers widely used for gene therapy today are viral carriers such as adenovirus, adeno-associated virus, retrovirus and non-viral carriers such as liposome, polyethyleneamine, etc.
As gene therapy strategies for controlling tumor cells, methods of using a tumor suppressor gene, using a replication-competent oncolytic virus, using a suicide gene and using an immunoregulatory gene, etc, have been used. The method of using a tumor suppressor gene is to treat cancer by delivering a tumor suppressor gene such as p53 into a patient specifically, where the gene is defected or deformed. In addition, the method of using a replication-competent oncolytic virus is to treat cancer by exploiting the damaged activity of tumor suppressor gene in tumor tissues by transferring a viral gene carrier that is able to be growing specifically in tumor cells to a human body. These two methods are the strategies to kill tumor cells directly. Alternately, the method of using a suicide gene is included in this category. A representative example of a suicide gene therapy is to treat disease by delivering a HSV-TK gene and chemical anticancer agents such as ganciclovir, which can induce death of tumor cells. On the contrary, the method to introduce an immunoregulatory gene is a kind of indirect treatment strategies, which carries one or more of the genes such as interleukin 12, interleukin 4, interleukin 7, gamma-interferon and tumor necrosis factor, etc, into a living body in order to provoke T cells to recognize tumor cells or induce apoptosis by blocking a tumor developing protein. On the other hand, the method to kill tumor cells by blocking nutrient supply by expressing angiogenesis inhibiting factors such as angiostatin or endostatin, etc, is also included in the category of indirect treatment strategies.
Metastatic spread is a critical determinant for the lethality of cancer. 67 kDa laminin receptor (67LR) is non-integrin type receptor embedded in plasma membrane and associated with cancer invasion and metastasis (Nelson, J. et al. The 67 kDa laminin receptor: structure, function and role in disease. Biosci. Rep. 28, 33-48 (2008)). 67LR is generated from dimerization of its 37 kDa precursor (37LRP) although molecular detail of this conversion process is not understood. 37LRP is identical to ribosomal subunit p40 that is involved in the formation of polysome (Auth, D. & Brawerman, G. A 33-kDa polypeptide with homology to the laminin receptor: component of translation machinery. Proc. Natl. Acad. Sci. USA 89, 4368-4372 (1992)). 67LR is often observed at high level in a variety of cancers (Nelson, J. et al. The 67 kDa laminin receptor: structure, function and role in disease. Biosci. Rep. 28, 33-48 (2008); Menard, S., Castronovo, V., Tagliabue, E. & Sobel, M. E. New insights into the metastasis-associated 67 kD laminin receptor. J. Cell. Biochem. 67, 155-165 (1997)). However, the regulator and molecular mechanism for the membrane residency of 67LR have not been determined yet. In this work, the present inventors found that lysyl-tRNA synthetase (KRS) enhances cell migration and cancer metastasis by stabilizing 67LR at plasma membrane.
KRS belongs to aminoacyl-tRNA synthetases (ARSs) that ligate their cognate amino acids and tRNAs for protein synthesis. These ancient enzymes show pleiotropic functions in addition to their catalytic activities (Park, S. G., Ewalt, K. L. & Kim, S. Functional expansion of aminoacyl-tRNA synthetases and their interacting factors: new perspectives on housekeepers. Trends Biochem. Sci. 30, 569-574 (2005)). Besides, several mammalian ARSs including KRS form a macromolecular complex (Lee, S. W., Cho, B. H., Park, S. G. & Kim, S. Aminoacyl-tRNA synthetase complexes: beyond translation. J. Cell. Sci. 117, 3725-3734 (2004); Han, J. M., Kim, J. Y. & Kim, S. Molecular network and functional implications of macromolecular tRNA synthetase complex. Biochem. Biophys. Res. Commun. 303, 985-993 (2003)), which serve as molecular reservoir (Ray, P. S., Arif, A. & Fox, P. Macromolecular complexes as depots for releasable regulatory proteins. Trends Biochem. Sci. 32, 158-164 (2007).), to control multiple functions of the component proteins. Human KRS contains unique N-terminal extension involved in the interactions with RNA and other proteins (Rho, S. B. et al. Genetic dissection of protein-protein interactions in multi-tRNA synthetase complex. Proc. Natl. Sci. Acad. USA 96, 4488-4493 (1999); Francin, M., Kaminska, M., Kerjan, P. & Mirande. M. The N-terminal domain of mammalian Lysyl-tRNA synthetase is a functional tRNA-binding domain. J. Biol. Chem. 277, 1762-1769 (2002)).